Francesco Redi and Controlled Experiments

Most people can name one 17th century Italian scientist who
challenged Aristotle's writings and changed
the way science was done for centuries to come. There were actually two!
Galileo was one. Francesco Redi was the other. Francesco Redi is famous
for his demonstration of the use of controlled experiments and his
challenge to the theory of spontaneous generation.

When a scientist designs an experiment it is important to eliminate as many unknowns
as possible. For instance, if one were trying to assess the health effects of a drug on
humans, there are many factors which may affect health..simply counting how many
of the patients get better or worse when given the drug is not good enough. We want
to know how many got better or worse specifically from the drug. One solution might be to introduce
a control to compare the drug-based tests against some standard case. In these drug-tests
one group is commonly given the drug and another group, the control group,
is given a placebo (commonly a sugar-pill with no known health effects). The subjects do not
know which type of pill they have been given. The drug results from the test group
can then be compared against those of the control group and we can get a better
idea of which effects result from the drug. This important advance in scientific methods
was introduced only 25 years after the death of
Galileo and only a few kilometres away from where he lived.

The Francesco Redi Experiment

Francesco Redi was able to disprove the theory that maggots could be
spontaneously generated from meat using a controlled experiment. Spontaneous generation, the theory that life forms
can be generated from inanimate objects, had been around since at least the time of Aristotle.
Francesco took eight jars, placed meat in all the jars, but covered four of the jars with muslin.
Maggots developed in the open jars but did not develop in the muslin-covered jars. Today controlled experiments are
commonly demanded by scientific journals and are sometimes legally required by regulatory bodies (especially for
pharmaceuticals). The image below is taken from Esperienze intorno alla generazione
degl' Insetti (p. 187) where Francesco Redi published a description of the experiment in 1668 (see sidebar for
digital copies of book).

We are taught that Galileo introduced the scientific method while Francesco Redi introduced
the controlled experiment. Both beliefs may be simplistic, however. Francesco Redi and Galileo
Galilei demonstrated their methods using very simple experiments then explained their
procedures in clear and compelling ways. This is why both are so important. But scientists before Redi
and Galileo had recognized the need to control variables and had described the sequence of steps described in
Galileo's experimental method. When Galileo
was still a young boy, Giuseppe Moletti, a professor at the University of Padua, conducted a series of experiments
on free fall by dropping weights in different
media (see Timeline of Classical Mechanics).
His test with free fall in water and air specified that the balls must be of the same
substance, weight and figure in order to remove doubt. In the same book, when Moletti described dropping balls of wood
and lead from a tower to demonstrate that free fall doesn't depend on weight (as
Aristotle had said) he was careful to eliminate size as a nuisance variable by conducting the experiment
with wooden balls of different sizes
[_1_]
.

Being careful to control for the known variables doesn't guarantee that you will get the correct results.
That is because "you don't know what you don't know". There might be variables that need to be
controlled that you don't even know exist. This is why the famous Tower of Pisa experiment
actually came up with incorrect results. Many consider the legend of the Tower of Pisa experiment to be a myth.
The experiment did occur. It was conducted by Vincenzio Renieri, a Catholic monk
(see Galileo's Battle for the Heaven's)
and not Galileo as is commonly thought.
Vincenzio was a friend of Galileo's. Like Moletti before him, Renieri, controlled for size when
he dropped two balls of the same size (one of wood and one of lead.) He came up
with the wrong results. There was almost 2 metres difference between the heavier and lighter balls when they
hit the ground. Galileo described similar results in some of his works. These scientists could not have known
that they needed to control for human physiology as well. Modern experiments with humans
dropping balls of markedly different weights show that there is a tendency to grip the heavier ball more tightly and
release it more slowly
[_2_]
.

Francesco Redi and the Galileo Affair

Francesco Redi lived during the time of the Galileo Affair. This event is
presented as evidence for the "the recurring clash between religion and science"
(see
Galileo's Battle for the Heaven's). Francesco Redi's experiences counter this interpretation.
Francesco Redi lived
a comfortable life in Florence, walking the same streets and working for the same people that Galileo
did (the Medicis). He died without encountering any problems with the Church.
Galileo's use of Italian instead of Latin was supposed to be a problem with the Church. But with
Francesco Redi, it wasn't. Any challenge to Aristotle was supposed to be a problem for the Church.
It was Aristotle who proposed life-forms such as maggots spontaneously generated, and it was Redi who
proved this false. The Galileo Affair was supposed to have caused the decline of science in Italy.
Redi's important advances in the scientific method happened only a short time after
the Galileo Affair in Galileo's adopted city.

The life and work of Francesco Redi provides cause to rethink the the Galileo Affair.
The Galileo Affair is commonly presented as proof of the conflict between science
and the church. Francesco Redi was defending scientific ideas that were as radical
as Galileo's. His experience with the church was completely different. Could
Galileo's personality and his personal and professional disagreements with the
other scientists of the day explain the difference? And leaving personality aside,
Francesco
Redi may have had a better argument against Aristotle because he used
better methods.

Scientific books in the time of Moletti and Galileo were often written as dialogues where one scientist was explaining things to another. In this book the protagonist describes an experiment where two balls of exactly the same weight, substance and shape are dropped through 100 paces of water and 100 paces of air. When the passive participant in the dialogue asks why they must be the same weight, substance and shape, the protagonist explains 'To remove causes of doubt'. Shortly after Moletti describes an experiment where two balls, one of twenty pounds of lead, and the other one pound are dropped from a tall tower, and that they both reach the ground at the same time. He then mentioned that he controlled for size by conducting the experiment with balls of wood of different sizes. Moletti's book is dated at 1576.

Thomas Settle describes an experiment by Dr. Donald Miklich who arranged for 51 students to perform repeated drops of balls with different weights then assessed the results. In 88 percent of the trials the lighter ball preceded the heavier one. This experiment used very specific experimental conditions and since the experimental conditions of the early free fall experiments were not always well described, the experiment might not properly relate to all experiments of the time.